Whatever you think its probably not big enough.
Mine is 36 feet deep and 38 feet wide. Ceiling is as high as 14 feet. Probably don't need that much ceiling over most of it, but that's more than enough for a lift big enough to handle a big bolt.
I've got three stalls full today and no room for the one I want to work on tomorrow. Twice the shop would be good right now!
You can check out my shop project at
www.MaxwellGarage.com.
